How to compress a PDF without losing quality

Almost every oversized PDF is oversized for the same reason: images. Text is famously compact in a PDF — a 200-page novel might fit in 1 MB — but a single high-resolution scan of a contract can balloon to 80 MB on its own. If you understand that, half of PDF compression already makes sense.

What “compress” actually does

PDF compressors generally do three things, in increasing order of aggressiveness:

1. Stream compression. Repackage internal objects so they take less disk space. This is free — no quality loss whatsoever.
2. Metadata stripping. Remove embedded author info, comments, and unused fonts. Mild and lossless for visual quality.
3. Image re-encoding. Decode images and re-encode them at a lower quality. This is where size really drops — and where quality can drop with it.

How to choose a compression level

For documents you’ll print, stay at the high end. For email attachments and web preview, the middle is almost always fine. For archives and quick previews where text legibility is all that matters, push to maximum and see if you notice.

The honest limits of online compression

Browser-based compression is excellent at the first two steps and competitive at the third. You can expect 40–80% savings on image-heavy PDFs and 5–15% on text-only ones. If a tool promises 90%+ on a typical text PDF, it is either lying or doing something to your file you wouldn’t consent to.

The PDFSamurai compressor offers three levels and runs entirely in your tab. If the result isn’t small enough, the only thing you’ve spent is a few seconds.